System and method for constant power LED driving and a redundancy dircuit thereof
A constant power DC light emitting diode (LED) driving system and method is disclosed. The system comprises a plurality of LED, a DC voltage source for LED current generation, and a constant-voltage and constant-current regulator for constant luminance control. A method and a redundancy circuit thereof for LED current detouring and LED luminance maintenance are also disclosed.
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1. Field of the Invention
The present invention is related to a system and method for light emitting diode (LED) driving, and more particularly to a system and method for constant power driving of which the driven LED(s) could be plural and has no need of special producing treatment for uniform luminance character.
2. Description of the Prior Art
LED is a p-n junction in semiconductor. Under a forward-bias driving, photons are created from the recombination of hole-electron pair at the p-n junction. The generating rate of photon numbers is therefore proportional to the forward-biased current through the p-n junction. Note that the larger forward-biased current is the higher emitting intensity. Conventionally, constant-voltage driving (
In recent years, the developing technologies of higher luminance and multicolor lead the appliances of LED to diversiform fields, such as light source, guidance lamp, LED back light module, signal lamp, display panel, and etc. In the near future, LED could be the major light source instead of traditional compact fluorescent lamp (CFL). In order to well control LED luminosity in the advanced appliances, an advanced LED driver satisfying the needs of circuit miniaturization, high stability, high efficiency, multi-LED driving supply, and battery life extension is imperiously needed. In conventional driving system, LED current cannot get a well control for suffering voltage spikes and ripples. The worse is the luminance character (I-V curve) has a wide distribution during mass production. For precisely LED luminance control, disposing an individual driver for every LED is a presumable solution. However, it will cost too much and waste chip space. Therefore, an advanced, robust, and economic LED driver is highly urgent in advanced luminance control.
SUMMARY OF THE INVENTIONThe main objective of the present invention is to provide a system and method for constant power LED driving, wherein a constant-voltage and constant-current regulator for precisely control of luminance power is used. With the constant-voltage and constant-current regulator and a DC voltage source, it becomes more convenient to use home electrical outlet on LED luminance driving. Further, the constant-voltage and constant-current regulator can clamp LED voltage and current both, and thereby the present invention is a robust and economic LED driving method and system even for multi-LED luminance control.
A further objective of the present invention is to provide a redundancy circuit, for combining with the LED set so as to provide an LED current detour to maintain LED luminance even under LED harm.
In order to achieve the said objectives, a LED driving method for constant luminance power according to the present invention comprises: applying a DC voltage VLD
A LED driving system for constant luminance power according to the present invention comprises: a DC voltage source 110 for DC voltage VLED
A redundancy circuit according to the present invention comprises a detour for LED current and a redundancy controller combined with the LED set so as to maintain the LED luminance without any effects of LED harm.
The present invention will be apparent after reading the detailed description of the preferred embodiments hereinafter in reference to the accompanying drawings.
An LED driving method for constant luminance power according to the present invention (please see
The first embodiment of providing DC voltage source in the LED driving method comprises: converting an AC voltage VAC to a DC voltage VDC through an AC/DC rectifier; converting the waved directional voltage VDC to the less waved output DC voltage VLED
A light emitting diode (LED) driving system for constant luminance power according to the present invention comprises: a DC voltage source 110 for DC voltage supply VLED
The constant-current circuit also comprises a current source 234 and a current sink 235. The current source is to generate a reference current Iref and the current sink is to clamp LED current ILED by the reference current Iref. The current source (please see
In order to avoid the terminating effect from harm LED during operation, a redundancy circuit (please see
Accordingly, as disclosed by the above description and accompanying drawings, the present invention surely can accomplish its objective to provide a constant power LED driving method and system with strictly voltage and current clamping, and may be put into industrial use especially for mass product.
It should be understood that various modifications and variations could be made from the teaching disclosed above by the persons familiar in the art, without departing the spirit of the present invention.
Claims
1. A light emitting diode (LED) driving method for constant luminance power comprises the following steps:
- (a) applying an output DC voltage VLED—DC from a DC voltage source on;
- (b) providing an LED set to generate an LED current ILED for LED luminance, wherein the LED current is controlled by; and
- (c) providing a constant-voltage and constant-current regulator for LED voltage differential and current clamping even under any tough situation such as voltage spike, voltage and current ripples, rising ambient temperature or other factors to change luminance characters (I-V curve).
2. The LED driving method according to claim 1, wherein the constant-voltage and constant-current regulator perform the following steps:
- (a) accepting the LED current though an output;
- (b) clamping the output voltage Vf and absorbing extra voltage during voltage spike, ripple and so on via a constant-voltage circuit; and
- (c) clamping the LED current ILED via a constant-current circuit.
3. The LED driving method according to claim 2, wherein the constant-voltage and constant-current regulator further performs the following steps:
- (a) outputting a reference current Iref via a reference current source; and
- (b) clamping the LED current ILED via the reference current.
4. The LED driving method according to claim 2, wherein the constant-voltage and constant-current regulator further performs adjusting the output voltage Vf by an input reference voltage Vref.
5. The LED driving method according to claim 3, wherein the constant-voltage and constant-current regulator further performs adjusting the reference current Iref by a setting voltage Vset and a setting resistor Rset.
6. The LED driving method according to claim 3, wherein the constant-voltage and constant-current regulator performs setting a luminance switch by a functional gate voltage wherein the luminance switch controls the LED set on-and-off in functional frequency to fit the anticipant luminance power.
7. The LED driving method according to claim 1, wherein the LED set consists of a single LED.
8. The LED driving method according to claim 1, wherein the LED set consists of a plurality of LED string in series.
9. The LED driving method according to claim 1, wherein the DC voltage perform: converting an AC voltage VAC to a DC voltage VDC through an AC/DC rectifier; and converting the waved DC voltage VDC to the less waved output DC voltage VLED—DC through a DC/DC converter in order to use home power source (AC voltage source) in LED driving.
10. The LED driving method according to claim 9, wherein the DC voltage source further perform: doubling the AC voltage VAC once to multi times through a plurality of double-voltage rectifier
11. The LED driving method according to claim 1, wherein the DC voltage source outputs VLED—DC is converted from a DC voltage VDC via a DC/DC converter.
12. The LED driving method according to claim 1, wherein the DC voltage source outputs VLED—DC is converted from an AC voltage VAC via an AC/DC converter in order to use home power source (AC voltage source) in LED driving.
13. A light emitting diode (LED) driving system for constant luminance power comprises:
- (a) a DC voltage source for DC voltage supply VLED—DC;
- (b) an LED set connected to the DC voltage source for generating LED current ILED; and
- (c) a constant-voltage and constant-current regulator connected with the LED set for LED voltage differential and current clamping even under any tough situation such as voltage spike, voltage and current ripples, rising ambient temperature or other factors to change luminance characters (I-V curve).
14. The LED driving system according to claim 13, wherein the constant-voltage and constant-current regulator further comprises:
- (a) an output for LED current ILED acceptor;
- (b) a constant-voltage circuit connected to the output for the output voltage Vf1 clamping; and
- (c) a constant-current circuit connected to the constant-voltage circuit for LED current ILED clamping.
15. The LED driving system according to claim 14, wherein the constant-voltage and constant-current regulator further comprises:
- (a) a current source consisting of a first output for steady reference current Ired output; and
- (b) a current sink consisting of a first input connected to the first output of current source for reference current Iref acceptor, and a second input connected with the constant-voltage circuit's output for LED current ILED acceptor, wherein the current through second input (i.e. ILED) is clamped as ILED=Iref*N, where N is a set value.
16. The LED driving system according to claim 14, wherein the constant-voltage and constant-current regulator further comprises: a positive input on the constant-voltage circuit for reference voltage Vref acceptor to control the value of clamping voltage Vf1.
17. The LED driving system according to claim 15, wherein the constant-voltage and constant-current regulator further comprises: a positive input on the current source for setting voltage Vset acceptor; and a second output on the current source connected with a setting resistor Rset to ground, wherein the second output voltage Vf2 is controlled by the setting voltage Vset and the outlet current of the first output on current source is Lref=Vf2/Rset.
18. The LED driving system according to claim 13, wherein the LED set consists of a single LED.
19. The LED driving system according to claim 13, wherein the LED set consists of a plurality of LED in series.
20. The LED driving system according to claim 13, wherein the DC voltage source comprises: an AC transformer providing an AC voltage VAC; an AC/DC rectifier converting the AC voltage VAC to a DC voltage VDC; and a DC/DC converter converting the waved DC voltage VDC to the less waved DC voltage source VLED—DC for using home power source on LED driving.
21. The LED driving system according to claim 20, wherein the DC voltage source further comprises: a plurality of double-voltage rectifier to double the AC voltage VAC once to few times before entering the AC/DC rectifier.
22. The LED driving system according to claim 13, wherein the DC voltage source outputs VLED—DC from converting a DC voltage VDC via a DC/DC converter.
23. The LED driving system according to claim 13, wherein the DC voltage source outputs VLED—DC from converting an AC voltage VAC via a AC/DC converter for using home power source on LED driving.
24. The LED driving system according to claim 16, wherein the constant-voltage and constant-current regulator further comprises: a constant-voltage transistor disposed between the output and the output of constant-voltage circuit; and a constant-voltage operation amplifier (Op-Amp) with its positive input connected to the positive input of constant-voltage circuit for the reference voltage Vref acceptor, with its negative input connected to the output of constant-voltage circuit, and with its gain output connected to the constant-voltage transistor's gate, wherein the constant-voltage transistor and Op-Amp form a feedback circuit for strictly clamping of output voltage Vf1 by a vary steady voltage, bandgap reference voltage Vref, and for dumping of extra voltage fluctuation on the constant-voltage transistor.
25. The LED driving system according to claim 16 further comprises: a constant-voltage transistor disposed between the DC voltage source and the LED set; and a constant-voltage operation amplifier (Op-Amp) with its positive input connected to the positive input of constant-voltage circuit for the reference voltage Vref acceptor, with its negative input connected to the output of constant-voltage circuit, and with its gain output connected to the constant-voltage transistor's gate, wherein the constant-voltage transistor and Op-Amp form a feedback circuit for strictly clamping of output voltage Vf1 by a vary steady voltage, bandgap reference voltage Vref, and for dumping of extra voltage fluctuation on the constant-voltage transistor.
26. The LED driving system according to claim 17, wherein the constant-voltage and constant-current regulator further comprises: a constant-current Op-Amp with its positive input connected to the positive input of current source for the setting voltage Vset acceptor, with its negative input connected to the second output of current source, and with its gain output connected to its negative input to form a feedback circuit, wherein the setting voltage Vset is coming from a bandgap reference voltage to clamp voltage on the second output of the current source as Vf2 for generating a steady current=Vf2/Rset; and a p channel current mirror consisting of one pair of common-gate p channel transistors with its input drain connected to its common-gate and the second output of the current source, and with its output drain connected to the first output of current source for current copy from the input drain to the output drain as reference current Iref=Vf2/Rset.
27. The LED driving system according to claim 26, wherein the constant-voltage and constant-current regulator further comprises: a constant-current transistor disposed between the second output of current source and the input of p channel current mirror, wherein the connection between gain output and negative input of the constant-current Op-Amp is terminated, and the connection between the gain output and gate of the constant-current transistor is connected up to absorb the extra voltage on Vf2 for steady current supply.
28. The LED driving system according to claim 15, wherein the constant-voltage and constant-current regulator further comprises: a first current mirror consisting of one pair of common-gate transistors with its input drain connected to the common-gate and the first input of the current sink, and with its output drain connected to the second input of current sink for LED current ILED acceptor, wherein the current through output drain of first current mirror (i.e. ILED) is clamped as N times of the current through input drain of first current mirror (i.e. Iref).
29. The LED driving system according to claim 28, wherein the constant-voltage and constant-current regulator further comprises: a second current mirror as same as the first current mirror with its input drain disposed between the first input of the current sink and input drain of the first current mirror for reference current acceptor, and with its output drain disposed between the second input of current sink and output drain of the first current mirror for LED current ILED acceptor, wherein the current through output drain of second current mirror (i.e. ILED) is clamped as N times of the current through input drain of second current mirror (i.e. Iref).
30. The LED driving system according to claim 28, wherein the constant-voltage and constant-current regulator further comprises: a pair of common-gate transistor of the current sink with its input drain disposed between the first input of the current sink and input drain of the first current mirror for reference current acceptor, and with its output drain disposed between the second input of current sink and output drain of the first current mirror for LED current ILED acceptor; and a switch transistor disposed on gate of the pair of common-gate transistor of the current sink, wherein LED's on-off can be controlled by the gate voltage and LED's luminance power can also be controlled by the on-off frequency of the functional gate voltage.
31. A redundancy circuit combined with a LED set, for using as a LED current detour circuit between any two nodes of the LED set for LED protection and LED luminance maintenance, wherein the detouring is controlled by a redundancy controller when the voltage differential between the two nodes is higher than a threshold voltage Vth.
32. The redundancy circuit according to claim 31, wherein the threshold voltage Vth is fixed.
33. The redundancy circuit according to claim 31, wherein the threshold voltage Vth is flexible.
34. The redundancy circuit according to claim 31, wherein the detour circuit is a silicon controlled rectifier (SCR) connected with the LED set in parallel whose gate is controlled by a gate current IG from the redundancy controller for detour opening.
35. The redundancy circuit according to claim 31, wherein the detour circuit comprises: a first metal oxide semiconductor field effect transistor (1st MOSFET) connected with the LED set in parallel whose gate is controlled by a gate voltage VG from the redundancy controller for detour opening; and a resistor disposed between gate and drain of the 1st MOSFET for setting the threshold voltage Vth.
36. The redundancy circuit according to claim 35, wherein the detour circuit further comprises: a resistor connected with source of the 1st MOSFET in series for setting voltage differential between two ends of the detour after detouring.
37. The redundancy circuit according to claim 35, wherein the detour circuit further comprises: a zener diode connected with source of the 1st MOSFET in series for setting voltage differential between two ends of the detour after detouring.
38. The redundancy circuit according to claim 35, wherein the detour circuit comprises: a second metal oxide semiconductor field effect transistor (2nd MOSFET) connected with source of the 1st MOSFET in series for setting voltage differential between two ends of the detour after detouring.
39. The redundancy circuit according to claim 31, wherein the detour circuit comprises: a zener diode connected with the LED set in parallel whose reverse bias current is conducted for detour opening when the voltage differential between the two nodes is higher than a threshold voltage Vth; and a resistor connected with the zener diode in series for threshold voltage Vth setting.
40. The redundancy circuit according to claim 31, wherein the detour circuit comprises: a transistor connected with the LED set in parallel whose gate is controlled by a gate current IG from the redundancy controller for detour opening and base is controlled by a base current from the redundancy controller for setting voltage differential between two ends of the detour after detouring; and a resistor disposed between gate and drain of the transistor for setting the threshold voltage Vth.
Type: Application
Filed: Nov 17, 2006
Publication Date: Mar 20, 2008
Applicant: VastView Technology Inc. (Hsinchu)
Inventors: Yuhren Shen (Hsinchu), Hung-Chi Chu (Hsinchu), Chun-Chi Chen (Hsinchu), Yu-Hsien Chang (Hsinchu)
Application Number: 11/600,852
International Classification: G09G 3/14 (20060101);